Irregular periods in your 40s: what changes and when to call

Your period used to show up on a familiar schedule. Lately the gap between cycles keeps shifting — shorter, longer, skipped — and the flow feels different too. That can be unsettling in your 40s.

Here's what reputable sources say about irregular periods around midlife, other common causes, and which bleeding changes are worth calling your doctor about.

What "irregular" often means

The NHS says the average gap between periods is around 28 days, though a bit shorter or longer can still be typical. Periods are irregular when that gap is less than 21 days or more than 35 days (NHS). ACOG describes a typical cycle length as between 24 and 38 days, with a normal period generally lasting up to 8 days (ACOG).

Those numbers are guides, not a self-diagnosis. What matters most is how your pattern has changed — and talking it through with a clinician.

How periods can change in perimenopause

The NHS says one of the first signs of perimenopause is usually a change to your periods (NHS).

ACOG says beginning in your 30s and 40s, estrogen from the ovaries begins to fluctuate, and a common sign of perimenopause is a change in your menstrual cycle: cycles may become longer or shorter than usual for you, you may skip periods, and flow may become lighter or heavier. Even so, ACOG says you should still report bleeding changes to your health care professional, because abnormal bleeding may be a sign of a problem (ACOG).

Mayo Clinic explains that as ovulation becomes more unpredictable, the time between periods may be longer or shorter, flow may be light to heavy, and you may skip some periods. Cycle length consistently different by seven days or more may line up with early perimenopause; gaps of 60 days or more may line up with late perimenopause (Mayo Clinic). Cleveland Clinic says irregular periods are generally the first sign of perimenopause — spotting at random, missed periods, or heavier or lighter bleeding (Cleveland Clinic). The Menopause Society describes early changes as often subtle, then later cycles that vary by 7 days or more, and in the late transition, skips of 60 days or more (The Menopause Society).

None of this means you should label yourself. If your cycle has changed, it's a normal thing to bring up with your doctor.

Pregnancy is still possible

Irregular does not mean "done." Mayo Clinic says that if you're still having periods, pregnancy is still possible, so use birth control until you've gone 12 months without a period if you don't want to get pregnant (Mayo Clinic). Cleveland Clinic says that until you've gone 12 consecutive months without a period, you should assume your body is still ovulating (Cleveland Clinic). The NHS is more specific about contraception: keep using it for 2 years after your final period if you're 40 to 49, or for 1 year if you're 50 or over (NHS). Ask your doctor before stopping.

A missed period can also be pregnancy. The NHS lists pregnancy among common causes of irregular periods (NHS). If there's any chance you could be pregnant, check with a test or your clinician — don't assume it's "just hormones."

It's not always perimenopause

Period changes have many possible explanations. The NHS lists common causes that include the start of menopause (usually between ages 45 and 55), pregnancy, some types of hormonal contraception, large weight changes, stress and anxiety, and exercising too much. Conditions such as polyendocrine metabolic ovarian syndrome (PMOS, formerly called PCOS) or thyroid problems can also cause irregular periods (NHS).

Cleveland Clinic notes other causes can include infection, fibroids, blood clotting disorders, polyps, and cancer (Cleveland Clinic). The Menopause Society says that to work out whether bleeding changes are a concern, it's important to talk with a healthcare professional (The Menopause Society). ACOG lists polyps, endometrial atrophy, endometrial hyperplasia, and endometrial cancer among causes an ob-gyn may evaluate (ACOG).

This blog won't tell you which cause fits you. That's a conversation for your doctor.

When to see a doctor

Please don't wait and wonder alone.

Mayo Clinic says see your healthcare professional if bleeding is very heavy, lasts longer than seven days, happens between periods, or periods are usually less than 21 days apart. If you've gone 12 months without a period and then start bleeding, tell your healthcare professional right away (Mayo Clinic). Cleveland Clinic adds: very heavy periods or large blood clots; changing pads or tampons every one to two hours; periods lasting several days longer than usual; spotting or bleeding between periods; bleeding after sex; or periods less than 21 days apart (Cleveland Clinic).

ACOG says it is not normal to have bleeding or spotting between periods or after sex, heavy bleeding, bleeding that lasts more days than usual, or bleeding after menopause (ACOG). The NHS irregular periods page advises seeing a GP if your periods are irregular or your normal pattern changes, your periods last longer than 7 days, or you have bleeding between periods (NHS). Its menopause page adds: contact a GP if your bleeding pattern has changed and you're bleeding more, not less, than before, or if you have not had a period for 12 months or more and you have any vaginal bleeding, even if it only happened once (NHS).

Before the appointment, a short note for a few cycles can help: start and stop dates, how heavy the flow felt, spotting, and new medicines. The NHS suggests using an app or a diary to keep track of your periods (NHS), and The Menopause Society says tracking bleeding on a calendar or app makes it easier to review (The Menopause Society). Tracking isn't for diagnosing yourself — it just makes the visit clearer.

The bottom line

Irregular periods in your 40s are common in perimenopause — cycles that stretch or shrink, lighter or heavier flow, skipped months. Other causes exist too, from pregnancy and contraception to thyroid problems, fibroids, polyps and more. Very heavy bleeding, bleeding that lasts longer than 7 days, bleeding between periods or after sex, periods less than 21 days apart, and any bleeding after 12 months without a period need prompt medical review. If your pattern has changed, talk to your doctor. You deserve clear answers — and a plan that fits your body.